Phytoplankton Community Structure Research Articles

Arctic phytoplankton microdiversity across the marginal ice zone: Subspecies vulnerability to sea-ice loss

Seasonal phytoplankton blooms are important Arctic phenomena, contributing to global primary production and biogeochemical cycling. The decline in sea-ice extent and thickness favors a longer open-water period with impacts on phytoplankton dynamics. Arctic net productivity is influenced by microalgae living associated with sea ice, with distinct species thought to be favored by ice-covered and ice-free waters. In this study, we investigated the phytoplankton community structure in Baffin Bay, a semi-enclosed sea where Arctic and North Atlantic water masses interact. We compared communities from the ice-free Atlantic-influenced eastern, the marginal ice zone, and the ice-covered Arctic-influenced western Baffin Bay. The community was characterized using 18S rRNA high-throughput amplicon sequencing and flow cytometry cell counting, and compared to environmental data collected during the Green Edge campaign. We sampled 16 stations grouped by sectors according to sea-ice cover. In the sectors associated with sea ice, phytoplankton formed a highly diverse community of smaller taxa, which contrasted with a low-diversity community in ice-free sectors, dominated by larger centric diatoms and Phaeocystis pouchetii adapted to high light/low nutrient conditions. Several phytoplankton species were flagged as indicators for the under-ice and marginal ice zone sectors, including ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also subspecies representatives of the early-blooming alga Micromonas polaris and the cryptophyte Baffinella frigidus. The strong association of certain taxa with under-ice and marginal ice zone sectors, including Pterosperma sp., Chrysochromulina sp., Micromonas polaris, and B. frigidus, suggest that they might be indicators of diversity loss due to ongoing sea-ice changes in Baffin Bay. We report new intra-species variability of Micromonas polaris suggesting that seasonal specialists could wax and wane over the bloom and non-bloom periods, highlighting the need for detailed year-long studies and the importance of microdiversity when assessing the diversity and distribution of polar phytoplankton.

Comparative Study on the Determination of Chlorophyll-a in Lake Phytoplankton by a YSI Multi-Parameter Water Quality Meter and Laboratory Spectrophotometric Method

Algal blooms caused by eutrophication are a major global problem, and the monitoring and prediction of algal densities in lakes are important indicators of eutrophication management. However, the reliability of the commonly used chlorophyll-a (Chl-a) to characterize phytoplankton density in lake environments needs to be further investigated. In this paper, we sampled and analyzed 365 samples from nine plateau lakes in Yunnan Province during the dry and rainy seasons. The Chl-a data measured by the laboratory spectrophotometric method and the portable YSI multi-parameter water quality meter (YSI) directly used in the field were compared, and regression analysis and correlation analysis with phytoplankton density were performed. Most of the Chl-a values measured by the laboratory instrument were greater than those measured by the YSI, and the correlation between the two methods was weak (0.492, p < 0.001). The correlation between Chl-a and phytoplankton density measured by the YSI reached 0.67 (p < 0.001) in the dry season, while the laboratory methods used to measure Chl-a to characterize phytoplankton density may have led to an overestimation of phytoplankton density due to nonspecific sources of Chl-a. However, both methods are relatively inaccurate for characterizing phytoplankton density. For different trophic states of lakes, nutrient concentration changes affect the Chl-a concentration of phytoplankton. During different seasons, changes in the fluorescence intensity of phytoplankton in response to environmental conditions prevent the YSI results from reflecting the authentic phytoplankton density. Furthermore, high species diversity can lead to inconsistent changes in Chl-a and phytoplankton because the content of Chl-a in individual cells of different phytoplankton is different. The relationship between Chl-a and phytoplankton density was species specific. Therefore, when applying Chl-a to characterize phytoplankton density in lakes, it is necessary to consider environmental conditions, phytoplankton community structure and other practical conditions. In addition, laboratory analytical methods and instrumental techniques and instruments need to be improved.

Land Use Impact on Water Quality and Phytoplankton Community Structure in Danjiangkou Reservoir

The composition and intensity of land use significantly influence the aquatic ecological environment, further affecting the physicochemical attributes of the water body, and indirectly modulating the phytoplankton community structure. This study centers around the Danjiangkou Reservoir, investigating the correlation between land use, water environment, and phytoplankton alongside varying intensities of anthropogenic activities, based on the review of land use, phytoplankton, and water quality data of 2021. Firstly, an analysis was conducted over five circular buffer zones generated around sampling points with radii set at 500 m, 1000 m, 1500 m, 2000 m, and 2500 m, wherein the intensity of human activity was categorized into low, medium, and high, in accordance with the human activity intensity level score (HAILS). This study proceeded to explore the correlation between land use and the water environment across different scales, compared phytoplankton density and community structure differences across varied levels of human activity, and analyzed the association between phytoplankton communities in the Danjiangkou Reservoir and environmental variables under various intensities. The findings showed: The land use within the 500 m circular buffer zone has the greatest impact on the water quality of the Danjiangkou Reservoir, especially with the increase in human activities leading to elevated nutrient levels in the water, thereby promoting the growth and reproduction of algae, and increasing the risk of algal blooms. This research scrutinizes the relationship between land use, water environment, and plankton under varying human activity intensities, serving as a foundation for environmental management sectors to make informed decisions and promote the sustainable development of the catchment water environment.

Dynamics of molybdenum and barium in the Bay of Brest (France) explained by phytoplankton community structure and aggregation events

Primary producers are essential organisms for marine ecosystems because they form the basis of food webs, produce half of atmospheric oxygen and are involved in various biogeochemical cycles. At the end of a bloom event, phytoplankton cells are known to produce organic compounds that act as a ‘cement’, allowing the cells to stick together and form large sinking structures called aggregates. These aggregates are microenvironments with chemical properties that are very different from the surrounding water. The main objective of this study was to determine how the temporal variations in cell assemblages over time and the formation of aggregates following a bloom affect the concentrations of molybdenum (Mo) and barium (Ba) in the water column, which are elements typically measured within accretionary hard tissues (e.g., mollusc shells) to track phytoplankton dynamics in the environment. To do so, we performed an environmental monitoring from March to October 2021 at Lanvéoc in the Bay of Brest (France) during which several biological (e.g., variations in phytoplankton assemblages) and chemical (e.g., chemical properties of the water column) parameters were measured once to twice per week. Our results show that spring and summer blooms of Gymnodinium, known to be enriched in Mo, could be one of the reasons explaining the particulate Mo enrichments in the water column. In addition, large phytoplankton aggregates transported a significant amount of Mo to the seafloor and associated suspension feeders. In contrast, the temporal variations in dissolved and particulate Ba concentration were strongly influenced by the formation of diatom blooms. Interestingly, there was a significant shift in Ba from the dissolved to the particulate fraction during the largest diatom bloom in late spring, associated with a significant Ba transport to the seafloor, which may be explained by the adsorption of this element onto diatom frustules. This study therefore highlights the impacts of phytoplankton on the dynamics of these elements in coastal ecosystems.

Responses of plankton community to threshold metal concentrations of cadmium and lead in a mesocosm experiment at Bay of Bengal

Metals are essential at trace levels to aquatic organisms for the function of many physiological and biological processes. But their elevated levels are toxic to the ecosystem and even brings about shifts in the plankton population. Threshold limits such as Predicted No Effect Concentration (PNEC - 0.6 μg/l of Cd; 2.7 μg/l of Pb), Criterion Continuous Concentration (CCC - 3.0 μg/l of Cd; 4.5 μg/l of Pb) and Criterion Maximum Concentration (CMC - 23 μg/l of Cd; 130 μg/l of Pb) prescribed for Indian coastal waters were used for the study. Short-term mesocosm experiments (96 h) were conducted in coastal waters of Visakhapatnam to evaluate responses of the planktonic community on exposure to threshold concentrations of cadmium and lead for the first time. Four individual experimental bags of 2500 L capacity (Control, PNEC, CCC & CMC) were used for the deployment and ambient water samples were analysed simultaneously to evaluate the impacts of the threshold levels in the natural waters. Chaetoceros sp. were dominant group in the control system whereas, Prorocentrum sp. Ceratium sp. Tintinopsis sp. Chaetoceros sp. and Skeletonema sp. were major groups in the test bags. Throughout the experiment the phytoplankton community did not show any significant differences with increased nutrients and plankton biomass (Chl-a <8.64 mg/m3). Positive response of plankton community was observed in the experimental bags. High abundance of diatoms were observed in PNEC, CCC & CMC bags at 48 h and the abundance decreased with shift in the species at 72–96 h. The catalase activity in phytoplankton (5.99 nmol/min/ml) and the zooplankton (4.77 nmol/min/ml) showed induction after exposure to PNEC. The present mesocosm study is confirmed that short-term exposure to threshold metal concentration did not affects the phytoplankton community structure in PNEC, but CCC and CMC affects the community structure beyond 24 h. The insights from this study will serve as a baseline information and help develop environmental management tools. We believe that long-term mesocosm experiments would unravel metal detoxification mechanisms at the cellular level and metal transfer rate at higher trophic levels in real-world environment.

Relationship between phytoplankton community structure and environmental factors in Yinchuan City water

The freshwater ecosystem, formed through the interaction between biological communities and the environment, serves as a vital resource for sustainable human development. Phytoplankton plays a pivotal role in environmental monitoring and ecological assessment, serving as a biological indicator in water quality assessment. However, the rapid urban development poses a significant threat to aquatic ecosystems, leading to environmental changes that alter phytoplankton community structures and degrade ecosystem functions. The research on the phytoplankton community structure and its correlation with environmental factors in Yinchuan remains insufficient. Therefore, it is imperative for Yinchuan's water ecosystem to comprehensively understand the phytoplankton community structure and identify the driving factors influencing the water ecological environment.A survey of phytoplankton was conducted in 40 stations across the Diannong River Basin, Yuehai Wetland, Baohu Wetland, and Hequanhu Wetland in Yinchuan in April 2023. The results revealed the presence of seven phyla and 211 species of phytoplankton in Yinchuan. Bacillariophyta comprised the majority of observed species, followed by Chlorophyta and Cyanophyta, with a smaller proportion of other species distributed throughout. Key influencing factors included total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH3-N), dissolved oxygen (DO), and transparency (SDD). Significant disparities were noted in both the Simpson index and Pielou's evenness index of the phytoplankton community.

Phytoplankton community structure and its driving factors in autumn in Jinan, China

Human activities often cause multiple impacts on aquatic ecosystems, including changes in water quality, biodiversity, community composition, etc. However, the effects of human activities on phytoplankton in highly urbanized aquatic ecosystems are poorly understood. In this study, we conducted an in-depth analysis of phytoplankton communities and water environment factors in the Jinan City watershed in September 2020, focusing on 18 water environment factors. We found that nitrate nitrogen, total nitrogen, total phosphorus, and phosphate were the key drivers affecting the quality of the water environment in the area through principal component analysis (PCA). The results of the phytoplankton investigation showed that 143 species of phytoplankton from 8 phyla were found in the Jinan watershed, dominated by Chlorophyta, Bacillariophyta, and Cyanobacteria, of which cyanobacteria were dominant in density, while cryptophytes were the first in biomass. The assessment of phytoplankton diversity showed that the Jinan City watershed had high biodiversity, with an average Shannon Wiener Diversity Index of 3.12. RDA analysis revealed that permanganate index, total phosphorus, bathymetry, chlorophyll a, pH, and phosphate were significantly correlated with the structure of the phytoplankton community. Comprehensive trophic index (TLI) analysis showed that most of the watersheds in Jinan were moderately eutrophic. These results provide essential information for understanding the water quality status and aquatic biodiversity in Jinan City watersheds and provide a scientific basis for water environment management and protection.

Interannual succession of phytoplankton community in a canyon-shaped drinking water reservoir during the initial impoundment period: Taxonomic versus functional groups

During the initial impoundment period of a canyon-shaped reservoir, the water body fluctuated violently regarding water level, hydrological condition, and thermal stratification. These variations may alter the structure of phytoplankton community, resulting in algal blooms and seriously threatening the ecological security of the reservoir. It is of great significance to understand the continuous changes of phytoplankton in the initial impoundment period for the protection of reservoir water quality. Therefore, a two-year in-situ monitoring study was conducted on water quality and phytoplankton in a representative canyon-shaped reservoir named Sanhekou and the interannual changes of phytoplankton community and its response to environmental changes during the initial impoundment period were discussed at taxonomic versus functional classification levels. The results showed that the total nitrogen and permanganate index levels were relatively high in the first year due to rapid water storage and heavy rainfall input, and the more stable hydrological conditions in the second year promoted the increase of algae density and the transformation of community, and the proportion of cyanobacteria increased significantly. The succession order of phytoplankton in the first year of the initial impoundment period was Chlorophyta-Bacillariophyta-Chlorophyta, or J/F/X1-P/MP/W1-A/X1/MP, respectively. And the succession order in the second year was Cyanobacteria/Chlorophyta-Bacillariophyta-Chlorophyta, or LM/G/P-P/A/X1-X1/J/G. Water temperature, relative water column stability, mixing depth, and pH were crucial factors affecting phytoplankton community succession. This study revealed the interannual succession law and driving factors of phytoplankton in the initial impoundment period and provided an important reference for the operation management and ecological protection of canyon-shaped reservoirs.

Daily process and key characteristics of phytoplankton bloom during a low-water level period in a large subtropical reservoir bay.

Reservoirs, heavily influenced by artificial management, often harbor phytoplankton assemblages dominated by cyanobacteria or dinoflagellates, triggering significant changes in aquatic ecosystems. However, due to limited sampling frequency and insufficient attention to species composition, the bloom processes and key characteristics of phytoplankton community structure have not been systematically elucidated. During the low-water level period when blooms are most likely to occur (June to September) in a tributary bay of the Three Gorges Reservoir, daily sampling was conducted to investigate phytoplankton community composition, identify significant environmental factors, and evaluate important structure characteristics of phytoplankton community. The results showed that Microcystis aeruginosa maintained a clear dominance for almost a month in stage 1, with low Shannon and evenness but a high dominance index. Phytoplankton total density and biomass decreased drastically in stage 2, but Microcystis aeruginosa still accounted for some proportion. The highest Shannon and evenness but the lowest dominance index occurred in stage 3. Peridiniopsis niei occurred massively in stage 4, but its dominant advantages lasted only one to two days. NH4-N was responsible for the dominance of Microcystis aeruginosa, while TP and PO4-P was responsible for the dominance of Peridiniopsis niei; however, precipitation contributed to their drastic decrease or disappearance to some extent. The TN : TP ratio could be considered as an important indicator to determine whether Microcystis aeruginosa or Peridiniopsis niei dominated the phytoplankton community. Throughout the study period, physiochemical factors explained more variation in phytoplankton data than meteorological and hydrological factors. Pairwise comparisons revealed an increase in average β diversity with stage progression, with higher β diversities based on abundance data than those based on presence/absence data. Repl had a greater effect on β diversity differences based on presence/absence data, whereas RichDiff had a greater effect on β diversity differences based on species abundance data. Co-occurrence networks for stage 1 showed the most complex structure, followed by stage 4, while the network for stage 3 was relatively sparse, although the overall community division remained compact. This study provides a useful attempt to explore the status and changes in phytoplankton community structure during the bloom process through high-resolution investigation.

Phytoplankton Communities’ Response to Thermal Stratification and Changing Environmental Conditions in a Deep-Water Reservoir: Stochastic and Deterministic Processes

Thermal stratification has become more extensive and prolonged because of global warming, and this change has had a significant impact on the distribution patterns of the phytoplankton communities. However, the response of phytoplankton community structures and assembly processes to thermal stratification is not fully understood. We predicted that the structure and assembly processes of phytoplankton communities would be affected by thermal stratification among water layers associated with environmental condition changes, reflecting certain patterns in temporal and spatial scales. Phytoplankton from Danjiangkou Reservoir were collected from October 2021 to July 2022 to verify this prediction. During the sampling period, Danjiangkou Reservoir remained thermally stratified with stability. The composition of the phytoplankton community in the surface layer significantly differed from that in both the thermocline and bottom layer. The phenomenon of thermal stratification affected the pattern of nitrogen and phosphorus distribution and, thus, the processes of the phytoplankton community structures. Deterministic processes had a greater influence on the assembly of the phytoplankton communities in the surface and bottom layers. In contrast, stochastic processes were more prevalent in the assembly of the thermocline phytoplankton community. The phytoplankton community within the thermocline layer exhibited a broader niche range than that in the surface and bottom layers, showing notable dissimilarity from that of the bottom layer. Canonical correspondence analysis (CCA) revealed that the vertical distributions of the phytoplankton communities were significantly correlated with NH4+-N, pH, and water temperature (WT). In summary, this study explained the distribution patterns of phytoplankton community structures and assembly processes in deep-water reservoirs during the stratification period. Additionally, the study explored the potential of using the distribution patterns of phytoplankton in stratified-state deep-water reservoirs under a subtropical–warm temperate climate as climate indicators in the context of global warming.

How uncertain and observable are marine ecosystem indicators in shelf seas?

Operational analysis and forecast products of shelf sea biogeochemistry often lack reliable information on uncertainty. This is problematic, as good quality uncertainty information is both requested by the product end-users and essential for data assimilation. To address this problem we developed a quality-assessed ensemble representation of many leading sources of uncertainty in a coupled marine physical-biogeochemical model of the North-West European Shelf. Based on these ensembles we have estimated the uncertainty of several marine ecosystem health indicators (MEHIs), acting as proxies for biological productivity, phytoplankton community structure, trophic fluxes, deoxygenation, acidification and carbon export. We have also evaluated how observable these MEHIs are from the most widely available observations of total chlorophyll (mostly from the surface), highlighting those MEHIs and locations that need to be better monitored. Our results show that the most uncertain and the least observable MEHI is the phytoplankton community composition, highlighting the value of its observations (and their assimilation) particularly in the UK regional waters. We demonstrate that daily operational estimates of the other MEHIs, produced by the Met Office, are fairly well constrained. We also quantify how much MEHI uncertainties are reduced when one substantially coarsens the MEHI spatial and temporal resolution, as in the global and/or climate applications.

Multiple biotic interactions establish phytoplankton community structure across environmental gradients

AbstractThe combination of taxa and size classes of phytoplankton that coexist at any location affects the structure of the marine food web and the magnitude of carbon fluxes to the deep ocean. But what controls the patterns of this community structure across environmental gradients remains unclear. Here, we focus on the North East Pacific Transition Zone, a ~ 10° region of latitude straddling warm, nutrient‐poor subtropical and cold, nutrient‐rich subpolar gyres. Data from three cruises to the region revealed intricate patterns of phytoplankton community structure: poleward increases in the number of cell size classes; increasing biomass of picoeukaryotes and diatoms; decreases in diazotrophs and Prochlorococcus; and both increases and decreases in Synechococcus. These patterns can only be partially explained by existing theories. Using data, theory, and numerical simulations, we show that the patterns of plankton distributions across the transition zone are the result of gradients in nutrient supply rates, which control a range of complex biotic interactions. We examine how interactions such as size‐specific grazing, multiple trophic strategies, shared grazing between several phytoplankton size classes and heterotrophic bacteria, and competition for multiple resources can individually explain aspects of the observed community structure. However, it is the combination of all these interactions together that is needed to explain the bulk compositional patterns in phytoplankton across the North East Pacific Transition Zone. The synthesis of multiple mechanisms is essential for us to begin to understand the shaping of community structure over large environmental gradients.

Phytoplankton abundance and biodiversity in adjacent estuaries: the importance of submarine groundwater discharge

AbstractA near-unique pair of adjacent bays in the karst region of western Ireland provided the opportunity to compare phytoplankton diversity and abundance in an area of submarine groundwater discharge (SGD) side by side with a ‘control’ region of similar size and with the same marine influences. Freshwater input to Kinvara Bay comes from the surrounding karst hinterland via a subterranean groundwater network, emerging at several sites within the inner bay as submarine groundwater discharge (SGD). Aughinish Bay in contrast has no connection to a SGD network and negligible overground fresh water input. Sampling was carried out in both bays during spring and neap tides over Winter, Spring/Summer and Summer/Autumn of 2016 and 2017. Comparison of the phytoplankton communities in the two bays showed higher diversity in Aughinish, while a bloom of Prorocentrum micans (Ehrenber, 1834), a brackish-water-tolerant marine dinoflagellate, was observed only in Kinvara. This work demonstrates how SGD can control phytoplankton community structure even in well-flushed macro-tidal bays and thus controls the biogeography at local scales.

Distinct differences of vertical phytoplankton community structure in mainstream and a tributary bay of the Three Gorges Reservoir, China.

The vertical distribution of phytoplankton plays a crucial role in shaping the dynamics and structure of aquatic communities. In highly dynamic reservoir systems, water level fluctuations significantly affect the physiochemical conditions and the phytoplankton community. However, the specific effects on the vertical characteristics of phytoplankton between the mainstream and the tributary bay of the reservoir remain unstudied. This study investigated the vertical aspects of phytoplankton density, biomass, α and β diversity through monthly sampling over two years in the mainstream (Chang Jiang, CJ) and a tributary bay (Xiang Xi, XX) of the Three Gorges Reservoir in China. Phytoplankton density and biomass were significantly higher in XX, indicating an increased risk of algal blooms in the tributary. The phytoplankton community in CJ showed more stable species-environment relationships, a lower Shannon index and a higher evenness index, suggesting a relatively simple structure and a more uniform distribution of phytoplankton among different water layers. Conversely, XX showed greater differences between water layers (higher β diversity), with significant negative correlations with water level and positive correlations with DO difference, dissolved silica (DSi) difference, and stratification. Peak phytoplankton density and biomass, as well as high β diversity in XX, occurred during periods of decreased water levels with strong stratification in spring and summer. A structural equation model complemented by path analysis revealed that a decrease in water level could increase β diversity either directly through internal processes with extended residence time or indirectly by modifying stratification and the vertical distribution of DSi in XX. Therefore, a proposed water quality management strategy for XX was to increase the water level or reduce β diversity by implementing artificial mixing during stratification periods. Overall, this study lies in its comprehensive investigation of the vertical characteristics of the phytoplankton community in both the mainstream and the tributary bay of the Three Gorges Reservoir, elucidating the significant impact of water level fluctuations and providing insights for targeted water quality management strategies in the tributary bay to mitigate potential ecological impacts.

Phytoplankton species composition as bioindicator in the largest fragmented channel of the Pearl River, China.

To test the serial discontinuity concept (SDC) predictions in a regulated river ecosystem, environmental parameters and phytoplankton community structure were determined in a subtropical river (China) which was regulated by 11 cascade dams. Our results showed that total phosphorus (TP) and silicate during the wet period in several dams supported the SDC predictions. Variations of phytoplankton species composition in several cascade dams, such as Datengxia (DTX) and Changzhou (CZ), also supported the SDC predictions. Moreover, the stations near the dams showed the maximum or minimum values of total species numbers in each cascade segment. Predictive model indicated that the types of phytoplankton decreased in the middle reaches, conforming to SDC predictions. In the whole system of cascading dams, an increase in silicate concentration and phytoplankton communities in the downstream was also consistent with SDC predictions. Therefore, these findings aligned with the SDC predictions in the aspects of both single dam and whole cascade dam system to some extent. In future research, our aim is to further investigate the effects of cascade damming on additional phytoplankton-related indices in this aquatic ecosystem. We hope to gather more comprehensive data to fully validate the SDC predictions.

Water quality assessment of river based on phytoplankton biological integrity index in rural areas of the upstream Citarum River, West Java, Indonesia

Abstract. Pratiwi D, Oktavia D, Sumiarsa D, Sunardi S. 2024. Water quality assessment of river based on phytoplankton biological integrity index in rural areas of the upstream Citarum River, West Java, Indonesia. Biodiversitas 25: 881-889. The deterioration of water quality in the upstream Citarum River is one of the consequences of agricultural practices characterized by fertilizer and pesticide runoff that disrupts the ecological balance of aquatic ecosystems. The research area was on agricultural land use in the Cihawuk segment, Kertasari, Bandung District. The present study attempts to community structure and assess the water quality using the biological indexes of rural areas in upstream Citarum River through phytoplankton studies. A purposive sampling technique was used to collect data on physico-chemical parameters and phytoplankton community structure from stations selected on the basis of agricultural land use. Furthermore, biological indexes such as pollution levels based on the Shannon Wienner diversity index (H'), Palmer algae index, and Diatomeae index are examined using the data community structure of phytoplankton. The findings show that the abundance of phytoplankton in rural areas is 4,105 cells/L. The community structure of phytoplankton was dominated by Coelastrum sp. and Trachellomonas sp. The Palmer algae index ranges from 23-26, indicating that the water was a highly organic pollutant. The pollution level of upstream Citarum River based on the diversity index shows moderately polluted water. Meanwhile, the diatomeae index showed less than 0.2, which sites water bodies were mesotrophic. Phytoplankton and their indexes serve as valuable tools for evaluating the quality of the water environment.

Decadal decreasing trend in biological carbon pump estimated from 234Th in the western subarctic North Pacific

We measured thorium-234 (234Th), particulate organic carbon (POC), and chlorophyll a in the western subarctic North Pacific surface layer in 1997–2008. 234Th, POC, and chlorophyll a in the surface layer showed clear seasonal changes. As a result of approximation by using a trigonometric function, 234Th export flux estimated from the deficiency of 234Th relative to 238U and the ratio of POC to particulate 234Th (POC/234ThP) indicated constant and decreasing trends in the study area from 1997 to 2008, respectively. POC export flux estimated from 234Th decreased in the study area, showing that the strength of the biological carbon pump in this region declined in the studied decade. The ratio of POC/chlorophyll a decreased during the term. These trends were possibly caused by a decline in not the biomass but particle size of phytoplankton. Our results suggest that not only the biological carbon pump but also phytoplankton community structure change in the western subarctic Pacific Ocean in a decade.

Grazing strategies determine the size composition of phytoplankton in eutrophic lakes

AbstractAlthough the general impacts of zooplankton grazing on phytoplankton communities are clear, we know comparatively less about how specific grazing strategies interact with environmental conditions to shape the size structure of phytoplankton communities. Here, we present a new data‐driven, size‐based model that describes changes in the size composition of lake phytoplankton under various environmental constraints. The model includes an ecological trade‐off emerging from observed allometric relationships between (1) phytoplankton cell size and phytoplankton growth and (2) phytoplankton cell size and zooplankton grazing. In our model, phytoplankton growth is nutrient‐dependent and zooplankton grazing varies according to specific grazing strategies, namely, specialists (targeting a narrow range of the size‐feeding spectrum) vs. generalists (targeting a wide range of the size‐feeding spectrum). Our results indicate that grazing strategies shape the size composition of the phytoplankton community in nutrient‐rich conditions, whereas inorganic nutrient concentrations govern phytoplankton biomass. Under oligotrophic regimes, the phytoplankton community is dominated by small cell sizes and the grazers have little to no impact. Under eutrophic regimes, dominating specialist grazers push phytoplankton towards small cells, whereas dominating generalist grazers push phytoplankton towards large cells. Our work highlights that trait‐based modeling, based on realistic eco‐physiological trade‐offs, represents a valuable tool for disentangling the interactive roles played by nutrient regimes and grazing strategies in determining the size compositions of lake phytoplankton. Ultimately, our study offers a quantitative basis for understanding how communities of lake phytoplankton may reorganize in the future in response to changes in nutrient levels and zooplankton grazing strategies.

Marine Heat Waves in the Indian Ocean: A Major Climate Impact on Marine Microalgae

A clearly defined, lengthy (five days or longer) period of extraordinarily high ocean temperatures is known as Marine Heat Waves (MHWs) (above the e0th percentile). These events significantly impact the structure, abundance, cell size, metabolic functions, physico-chemical interactions between microalgae cells and their surroundings in the Indian Ocean. In the tropical Indian Ocean, the average sea surface temperature (SST) increased by 1.0°C (0.15°C/decade) on average between 1951 and 2015, while the global average SST warmed by roughly 0.7°C (0.11 °C/decade). This resulted from the incidence of Marine microalgal bloom MMBs (including Harmful Algal Bloom) and the number of causal taxa may grow as SST increases. Trichodesmium and Noctiluca contributed 34.4% and 31.8%, respectively, to the overall blooms. Such a heating phenomenon also triggers the dominance of small-sized algal cells, harmful diatoms and pico-plankton. The present paper reviews the Indian as well as global episodes of MHWs such as Western South Atlantic, North-East Pacific, Western Australia, Alaskan Sea etc. and their impact on phytoplankton. The combination of warming and heatwaves triggers blooms of buoyant cyanobacteria and its combined impacts of MHWs and ocean warming/acidification on phytoplankton community structure have not been fully studied in the Indian Ocean.

HPLC validation as a management tool in artificial water storage ponds

Pigment analysis through high-performance liquid chromatography (HPLC) offers a faster and more replicable study of the phytoplankton community structure than traditional taxonomy, but its application to small-sized freshwater ecosystems is infrequent. We carried out a taxonomy-based validation for the application of HPLC to the management of two artificial water storage ponds. We also investigated the error and variability sources that affected the relationships between calculated biovolumes of phytoplankton groups and associated pigment concentrations. For both qualitative and quantitative approaches, agreement was obtained between techniques that consistently identified biomass peaks and structural trophic differences between the ponds. Considering the most relevant pigment to biovolume ratios for total biomass, and partial biomass proxies of green algae and fucoxanthin containing algae, a decreasing tendency was obtained as total and partial biomass increased in all the studied models. Bidirectional variability affecting these relationships scaled under high biomass conditions and suggested a better suitability of HPLC application under oligotrophic conditions, which is in line with previous studies. Additionally, pigment data was able to identify mean stored volume as the main environmental factor that drove trophic differences between the ponds. We conclude that HPLC is accurate not just for monitoring purposes, but to carry out ecosystem-level assessments in artificial ponds. Therefore, we endorse the use of HPLC as part of the monitoring networks in small-sized freshwater ecosystems.